Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 211808
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1007 AM PST SUN DEC 21 2014

.SYNOPSIS...MILD AND WET WEATHER CONTINUES TODAY. RAIN IS EASING FROM
NORTH TO SOUTH AS A COLD FRONT DROPS DOWN INTO THE REGION. THE
HEAVIEST RAIN THROUGH THE REST OF TODAY WILL BE OVER THE LANE COUNTY
CASCADES AND CENTRAL OREGON COAST RANGE. PRECIPITATION DECREASES
FURTHER TONIGHT AND MONDAY AS THE COLD FRONT STALLS OVER CENTRAL
OREGON AND WEAKENS AND AN UPPER RIDGE BUILDS OVER THE NORTHEAST
PACIFIC. MULTIPLE RIVERS HAVE REACHED FLOOD STAGE...AND FLOOD IMPACTS
WILL CONTINUE INTO TONIGHT. THERE MAY ALSO BE TIDAL OVERFLOW ISSUES
TODAY DUE TO A HIGH TIDAL CYCLE AND THE INCREASED FLOW IN THE COASTAL
RIVERS. A COLDER AIR MASS WILL SETTLE OVER THE PACIFIC NORTHWEST LATE
NEXT WEEK WITH SNOW DOWN INTO AT LEAST THE CASCADE FOOTHILLS AND
COAST RANGE AS A COOLER SYSTEM FROM THE NORTHWEST MOVES THROUGH WED
AND WED NIGHT. A QUIET WEATHER PERIOD APPEARS TO BE IN STORE LATE
NEXT WEEK AS UPPER LEVEL RIDGING BUILDS OVER THE PAC NW.

&&

.SHORT TERM...TODAY THROUGH TUE NIGHT...
AN ATMOSPHERIC RIVER PRECIPITATION EVENT HAS BROUGHT WIDESPREAD HEAVY
RAINFALL TO SW WASHINGTON AND NW OREGON OVER THE WEEKEND. HOWEVER THE
EVENT IS BEGINNING TO WIND DOWN AT THIS POINT. WATER VAPOR AND IR
SATELLITE IMAGERY SHOW THAT THE BEST MOISTURE HAS MOSTLY PUSHED
ONSHORE AT THIS POINT...WITH THE BEST REMAINING MOISTURE NOW FOCUSED
OVER CENTRAL AND SOUTHERN OREGON. A COLD FRONT IS DROPPING DOWN INTO
THE REGION FROM THE NORTH TODAY...WHICH IS CUTTING OFF THE SUPPLY OF
SUB-TROPICAL MOISTURE FROM NORTH TO SOUTH. THE WESTERLY MID LEVEL
WINDS THAT HAVE BEEN CREATING SIGNIFICANT OROGRAPHIC FORCING ALONG
THE HIGHER TERRAIN OF THE CASCADES AND COAST RANGE ARE ALSO
DIMINISHING BEHIND THE FRONT. A LOOK AT THE LATEST NWS DOPPLER RADAR
STILL SHOWS PLENTY OF PRECIPITATION STILL OCCURRING OVER THE HIGHER
TERRAIN...BUT THE HEAVIEST PRECIP IS NOW CONFINED TO THE CASCADES
SOUTH OF MT HOOD. AS WE GO THROUGH THE REST OF TODAY AND
TONIGHT...THE COLD FRONT WILL CONTINUE TO WORK ITS WAY SLOWLY SOUTH
AND THE HEAVIEST PRECIPITATION WILL BE CONFINED MAINLY TO THE LANE
COUNTY CASCADES AND CENTRAL OREGON COAST RANGE. THE HIGH RAINFALL
TOTALS FROM THIS EVENT HAVE CAUSED NUMEROUS RIVERS TO REACH FLOOD
STAGE. THESE FLOODING CONCERNS WILL CONTINUE THROUGH THE REST OF
TODAY AND INTO TONIGHT. SEE THE HYDROLOGY SECTION BELOW FOR MORE
DETAILS.

THE HIGH TIDE TODAY WILL BE OF ABOUT THE SAME MAGNITUDE AS
YESTERDAY...AND WITH MUCH HIGHER FLOWS ON THE COASTAL RIVERS. SINCE
WE EXPERIENCED SOME ISSUES YESTERDAY...CONFIDENCE IS FAIRLY HIGH THAT
AT LEAST SOME MINOR TIDAL OVERFLOW IMPACTS WILL BE OBSERVED TODAY.
LOW LYING AREAS NEAR WILLAPA BAY...TILLAMOOK BAY...DEPOE
BAY...WALDPORT...AND FLORENCE...ALONG WITH STRETCHES OF HIGHWAY 101
ALONG THE COAST...MAY EXPERIENCE MINOR TIDAL OVERFLOW ISSUES DURING
THE HIGH TIDE AROUND 11 AM. PEAK IMPACTS ARE LIKELY BETWEEN ABOUT 9
AM AND 3 PM. WITH RIVERS CONTINUING TO RUN HIGH...THE MIDDAY HIGH
TIDE ON MONDAY MAY AGAIN CAUSE SOME MINOR ISSUES.

PRECIPITATION WILL REALLY BEGIN TO TAPER OFF TONIGHT AS THE COLD
FRONT PUSHES INTO CENTRAL OREGON AND UPPER LEVEL RIDGING BEGINS TO
BUILD INTO THE PAC NW. THE COLD FRONT EVENTUALLY STALLS AND WEAKENS
OVER CENTRAL OREGON BY EARLY MON MORNING. TEMPERATURES AND SNOW
LEVELS WILL DROP BEHIND THE COLD FRONT...WHICH SHOULD ALLOW FOR
SEVERAL INCHES OF ACCUMULATING SNOW FOR THE HIGHEST CASCADE PASSES
TONIGHT. EXPECT QPF TO BE LIMITED...SO ACCUMULATIONS SHOULD REMAIN
BELOW ADVISORY CRITERIA.

THE STALLED BAROCLINIC ZONE OVER CENTRAL OREGON MAY ALLOW PRECIP TO
CONTINUE INTO MON MORNING OVER THE SOUTHERN PORTIONS OF OUR FCST AREA.
HOWEVER...RAINFALL SHOULD BE ON THE LIGHT SIDE WITH THE BUILDING
UPPER LEVEL HEIGHTS. THE BAROCLINIC ZONE THEN MOVES NORTH AS A WEAK
WARM FRONT LATER MON...WHICH MAY SPREAD THE LIGHT PRECIP FURTHER
NORTH.

THE NEXT SYSTEM STARTS TO DROP INTO THE PACIFIC NORTHWEST ON
TUESDAY...BUT ITS MAIN EFFECTS OF MORE RAIN AND SIGNIFICANTLY
LOWERING SNOW LEVELS WILL OCCUR MAINLY ON WEDNESDAY. PYLE

&&

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...
TUESDAY NIGHT THROUGH SATURDAY...MODELS REMAIN CONSISTENT IN
FLATTENING AN UPPER LEVEL RIDGE LATE TUESDAY INTO WEDNESDAY. THERE
ARE SOME MODEL DISCREPANCIES CONCERNING HOW FAR SOUTH THE NEXT
SHORTWAVE WILL MOVE INTO THE PACIFIC NORTHWEST...BUT OVERALL AN UPPER
LEVEL TROUGH WILL SAG SOUTH AND MOVE INLAND EARLY WEDNESDAY. THIS
WILL USHER IN ANOTHER BATCH OF COOL AND RAINY CONDITIONS...WITH SNOW
LEVELS DROPPING TO NEAR 2000 FT SO EXPECT SNOW SHOWERS OVER CASCADE
PASSES RIGHT IN TIME FOR HOLIDAY TRAVEL. AGAIN...HOLIDAY TRAVELERS
HEADED OVER THE CASCADE PASSES WILL CERTAINLY NEED TO MONITOR THE
FORECAST. LINGERING MOISTURE CONTINUES INTO CHRISTMAS DAY...BUT WILL
LIKELY BE OCCASIONAL SHOWERS WITH PARTLY CLOUDY SKIES FOR THE MOST
PART. COLDER NORTHERLY FLOW PERSISTS INTO EARLY NEXT WEEKEND...WITH
DRIER CONDITIONS EXPECTED FOR FRIDAY. A NEW DEVELOPMENT IN THE 12Z
MODEL RUNS HAS BEEN ANOTHER SHORTWAVE DISTURBANCE DROPPING SOUTH OVER
THE FORECAST AREA LATE FRIDAY... BRINGING A THREAT FOR RAIN AND SNOW
ON THE MOUNTAINS. /27
&&

.HYDROLOGY...A SLOW DECREASE IN RAIN RATES THIS MORNING IS EXPECTED
TO CONTINUE TODAY. THE RAIN WILL TAPER OFF THIS AFTERNOON THROUGH
MONDAY. NUMEROUS FLOOD WARNINGS ARE ALREADY IN EFFECT...BUT ALL
LOCAL RIVERS ARE EXPECTED TO REMAIN BELOW MAJOR FLOOD STAGE. COASTAL
RIVERS HAVE CRESTED OR ARE CURRENTLY CRESTING AND MOST WILL FALL
BELOW FLOOD STAGE THIS AFTERNOON. WILLAMETTE TRIBUTARIES WILL
CONTINUE TO RISE AND ANY FLOODING WILL GENERALLY BEGIN LATER TODAY.
FLOODING ALONG THE MAINSTEM WILLAMETTE LOOKS UNLIKELY AT THIS POINT.
SEE THE LATEST WARNINGS AND FLOOD STATEMENTS AT
WWW.WEATHER.GOV/PORTLAND (LOWER CASE) FOR ADDITIONAL DETAILS. BOWEN

&&


.AVIATION...MODERATE ONSHORE FLOW CONTINUES THIS MORNING WITH
ABUNDANT MID AND HIGH CLOUDS. HOWEVER...GENERALLY VFR ACROSS THE
INTERIOR WITH A FEW MVFR POCKETS. SIMILARLY...GENERALLY MVFR
CONDITIONS ALONG THE COAST WITH LOCAL IFR. RAIN GENERALLY
DECREASING BUT MANY AREAS WILL SEE SHOWERS AT TIMES THROUGH THE
AFTERNOON. EXPECT LITTLE CHANGE TODAY THROUGH EARLY TONIGHT AND
HIGHER TERRAIN...ESPECIALLY CASCADES...WILL REMAIN OBSCURED IN
CLOUDS AND PRECIP THROUGH TONIGHT.

KPDX AND APPROACHES...MOSTLY VFR THROUGH HIS EVENING...WITH
SHOWERS AT TIMES. EXPECT OCCASIONAL BUT BRIEF PERIODS OF MVFR CIGS
THROUGH ABOUT 21Z. THEN INCREASING POTENTIAL FOR SOME LOWER MVFR
CIGS DEVELOPING AFT 04Z. CULLEN

&&

.MARINE...WINDS 15 TO 20 KT THIS MORNING WILL GRADUALLY EASE AND
BECOME MORE W TO NW. SEAS RUNNING 14 TO 16 FT THIS AM...BUT THESE
TOO WILL BE SLOWLY SUBSIDING TODAY BUT LIKELY HOLD AROUND 11 TO 12
FT THROUGH AT LEAST MIDWEEK. ANOTHER QUICKLY MOVING FRONT WILL
ARRIVE LATER TUE AND WED...WITH SOME POTENTIAL FOR BRIEF PERIOD OF
WINDS GUSTING NEAR 25 KT.  CULLEN

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...COASTAL FLOOD ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR
    CENTRAL OREGON COAST-NORTH OREGON COAST.

WA...FLOOD WATCH THROUGH MONDAY AFTERNOON FOR CENTRAL COLUMBIA RIVER
     GORGE-GREATER VANCOUVER AREA-I-5 CORRIDOR IN COWLITZ COUNTY-
     SOUTH WASHINGTON CASCADE FOOTHILLS-SOUTH WASHINGTON
     CASCADES-SOUTH WASHINGTON COAST-WESTERN COLUMBIA RIVER
     GORGE-WILLAPA HILLS.

     COASTAL FLOOD ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR SOUTH
     WASHINGTON COAST.

PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 PM PST MONDAY
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT
    60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 9 AM
     PST MONDAY.

&&

$$

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS
COMMONLY REFERRED TO AS THE FORECAST AREA.



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